Air-cooling tower

ABSTRACT

A cooling tower is described employing a heat exchanger and duct means defining a passage for directing the air over the heat exchanger for cooling same. The duct means have upper and lower air intake orifices, the former being positioned a substantial distance above ground level and the latter being positioned substantially at ground level. Means are provided for selectively drawing air into the duct means through either of said orifices.

This invention relates generally to cooling towers and, moreparticularly, to an improved cooling tower capable of taking advantageof variations in the adiabatic lapse rate near ground level.

Cooling towers are often employed in connection with various kinds ofindustrial or power generating equipment. For example, a cooling towermay be employed in a closed cycle gas turbine system for the purpose ofcooling the gas prior to compression.

Typically, a dry-cooling tower employs suitable heat exchange structuresuch as tubes or similar conduits arranged to provide an interfacebetween the material being cooled and flowing air. A wet cooling towermay employ means to facilitate evaporation of a coolant liquid. Ineither case, air may be caused to flow by natural convection or may becaused to flow in forced air systems by fans. For the purpose ofdirecting the air through the heat exchanger, the heat exchanger isenclosed in a duct system of suitable shape. For example, oneparticularly useful duct system includes a main duct comprising an opentop funnel in which the heat exchanger is placed. The warming effect ofthe heat exchanger on the air results in an natural convection flow ofair upwardly through the funnel, drawing additional air inwardly nearthe bottom of the funnel through an annular intake region.

The rate of variation in the temperature of the atmosphere with distanceabove the ground is generally referred to as the adiabatic lapse rate.Ideally, this involves a substantially linear decline in temperaturewith distance above the ground, typically several degrees Fahrenheit perthousand feet.

During mid-day, solar heating from the sun heats the ground to atemperature higher than the air above the ground. By convection, the hotground heats the air immediately above the ground to a temperature abovethe normal adiabatic lapse rate temperatures. This effect isparticularly pronounced in summer during mid-day in barren, semi-arid ordesert areas where cover is minimal. At night, the above describedsuper-adiabatic lapse rate effect frequently reverses and becomessub-adiabatic. The ground cools by radiation to the night sky to atemperature lower than the air just above the ground. This means thatthe air a substantial distance above the ground may actually be warmerthan that at the surface, and that the coolest air available for a heatexchanger frequently is at ground level at night, whereas it is aboveground level during the hot part of the day.

It is an object of the present invention to provide an improved coolingtower.

Another object of the invention is to provide a cooling tower capable ofutilizing the effect of the super-adiabatic or sub-adiabatic lapse rateat ground level.

Another object of the invention is to provide a cooling tower in whichthe coolest possible air is supplied to the heat exchanger under alloperating conditions.

Various other objects of the invention will become apparent to thoseskilled in the art from the foregoing description, taken in connectionwith the accompanying drawings wherein:

FIG. 1 is a graph illustrating the variation in air temperature versusheight above the ground and illustrating the variation in adiabaticlapse rate which may occur at a typical cooling tower location;

FIG. 2 is a schematic full section view illustrating a dry-cooling towerconstructed in accordance with the invention;

FIG. 3 is a full section schematic view illustrating a furtherembodiment of the invention;

FIG. 4 is a full section schematic view illustrating a still furtherembodiment of the invention; and

FIG. 5 is a full section schematic view illustrating still anotherembodiment of the invention.

Very generally, the cooling tower of the invention comprises a heatexchanger 11 and duct means 12 defining a passage for directing air overthe heat exchanger for cooling same. The duct means include an upper airintake orifice 13 positioned a substantial distance above ground level14. The duct means further include a lower air intake orifice 15positioned substantially at ground level. Means 16 are provided forselectively drawing air into the duct means through the upper air intakeorifice or through the lower air intake orifice.

Referring now more particularly to FIG. 1, a graph is presented in whichair temperature is plotted versus height above ground level. The line 21represents the normal adiabatic lapse rate which is approximately 4° Fper 1000 feet. If this line 21 is extrapolated to ground level, the airtemperature at ground level is thereby represented at the point 23.During mid-day as one approaches ground level, the rate of temperaturerise increases greatly at a super-adiabatic rate as shown by the dottedline 25 to the right of thhe solid line 21. The temperature at groundlevel during mid-day is thereby represented by the point 27, thedifference in temperature between the points 23 and 27 therebyrepresenting the effect of ground heating at mid-day. At night, theadiabatic lapse rate frequently reverses as illustrated by the dottedline 29 to the left of the solid line 21 in FIG. 1. The line 29intersects the gound level at the point 31 and the difference betweenthe temperature at the point 23 and the temperature at the point 31represents the effect of ground cooling during the night time.

Referring now more particularly to FIG. 2, a dry-cooling towerconstructed in accordance with the invention is shown which is capableof taking advantage of the variations described above to minimize thetemperature of the air flowing through the heat exchanger. Moreparticularly, the cooling tower includes a heat exchanger which is ofsuitable configuration depending upon the particular fluid being cooledand depending upon the particular operating temperatures desired. Theheat exchanger 11 may therefore consist of a plurality of tubes orsimilar conduits arrayed in loops or convolutions to provide the desiredheat exchange surface.

For the purpose of confining the flowing cooling air to the heatexchanger 11, the duct means 12 include a funnel 33, the upper and lowerends of which are open. Air is drawn in through the open lower end ofthe funnel 33 and exits through the open top end of the funnel 33 asindicated by the solid line arrows and by the dotted line arrows. Thefunnel 33 is supported slightly above ground level by a plurality ofstruts 35 which thereby form an annular intake region just above theground level 14.

In the embodiment illustrated in FIG. 2, the duct means 12 furtherinclude an annular sleeve 37, which is supported by suitable struts 39,surrounding the funnel 33 coaxially thereof. The sleeve 37 is shaped ina flared configuration to match the configuration of the funnel 33 whichit surrounds. The axial length of the sleeve 37 is substantially lessthan the axial length of the funnel 33 to prevent recycling of the airdischarged from the top of the funnel, as described in greater detailbelow.

Means 16 are provided for selectively drawing air into the duct meansthrough either the upper annular opening 13 between the sleeve 37 andthe funnel 33 or through the annular opening 15 between the lower edgeof the sleeve 37 and the ground 14. The means 16 include a movable valveor gate 41 of suitable configuration and which is capable of moving fromthe position shown by the solid lines (in which the annulus formedbetween the lower edge of the sleeve 37 and the lower edge of the funnel33 is closed) to the position shown by the dotted lines (in whichopening 15 is closed and the previously described annulus is open).Movement is effected by a suitable electric motor 43 controlled by amotor drive control 45.

The motor drive control is connected to a temperature sensor 47 and to atemperature sensor 49. The temperature sensor 47 is positioned at groundlevel and the temperature sensor 49 is positioned at the level of theair intake 13. When the motor control unit 45 senses that thetemperature at the temperature sensor 47 is greater than that at thetemperature sensor 49, the valve element 41 is moved to the positionshown by the dotted lines. In this case, the air drawn into the ductmeans through the opening 13 passes down through the region between thesleeve 37 and the funnel 33, around beneath the lower edge of the funnel33 as shown by the dotted arrows, and then up through the funnel 33 pastthe heat exchanger 11, being discharged from the open top of the funnel.

When the temperature sensed by the temperature sensors 47 and 49indicates that the temperature at ground level 14 is lower, the motorcontrol unit 45 causes the motor 43 to move the valve element 41 to theposition shown by the solid lines. As shown by the solid lines, air thenenters the duct means 12 through the opening 15, passing beneath thelower edge of the funnel 33 and up through the funnel over the heatexchanger to be discharged through the open top.

Referring now to FIG. 3, a further embodiment of the invention isillustrated. Those parts of the embodiment of FIG. 3 which are similarin function and structure to parts in the embodiment of FIG. 2 have beengiven identical reference numbers preceded by a 1.

The cooling tower of FIG. 3 is of the natural convection type employingan open top funnel 133 as part of the duct means 112 enclosing the heatexchanger 111. To simplify the drawing, the motor, motor control andtemperature sensors are not illustrated in FIG. 3 but it is to beunderstood that they may be employed.

In the embodiment shown in FIG. 3, the upper air inlet opening 113 isformed at the top of a stack 136 which is in communication with theannular space beneath the lower edge of the funnel 133 by a conduit 138.

The conduit 138 terminates in an annulus 142 which surrounds the annularspace beneath the lower edge of the funnel 133 and the ground 114. Thevalve means 141 are of a suitable configuration such that, in theposition illustrated in solid lines, the conduit 138 is blocked at theend thereof adjacent the annulus 142. The annulus 142 is of relativelyshort axial length and, when the valve means 141 are in the positionillustrated in the solid lines, the top of the annulus is open so thatair may be drawn therein from adjacent ground level as illustrated bythe solid arrows.

When the air is cooler a substantial distance above ground level, thevalve means 141 are adjusted such that the conduit 138 communicates withthe annulus 142 and such that the upper portion of the annulus 142 isclosed as indicated by the dotted lines in FIG. 3. In this condition,air is drawn into the funnel 133 through the orifice 113, stack 136 andthe conduit 138, as illustrated by the dotted arrows. Thus, the airflowing over the heat exchanger 111 is drawn from a positionsubstantially higher than ground level.

More than one inlet stack may be used, thus insuring that at least oneof the stacks may be positioned upwind of the hot exhaust air emanatingfrom the top of the funnel 133 and therefore will always provide a coolinlet supply. Suitable regulation of the dual stacks may then beeffected to insure there is no short circuiting of the hot exhaust air.Naturally, the stacks are placed a distance from the funnel 133sufficient to avoid interaction with the hot exhaust air by the upwindstack.

In FIG. 4, a forced air convection cooling tower is illustrated in whichthe means for selectively drawing air into the duct means through theupper or lower air intake orifices include both valve means 241 and fans242. Instead of being positioned as shown, a single fan could be placedin the funnel 233 itself. The other elements of the cooling towerillustrated in FIG. 4 which are similar in design and function toelements in FIG. 2 have been given identical reference numbers precededby a 2.

In the illustrated embodiment, two ducts 238 communicate with a plenum240 beneath the heat exchanger 211. Stacks 236 are provided definingupper air inlet openings 213 positioned a substantial distance above theground and which are spaced a sufficient distance from the open top ofthe funnel 233 so as to avoid interference with the hot exhaust air. Thelower air inlet openings are formed in the conduits 238 as illustratedat 215. With the valve means shown in the position illustrated in solidlines, rotation of the fans 242 causes air to be drawn in through thelower air inlet openings 215 and into the plenum 240. From there itpasses upwardly through the heat exchanger 211 to be discharged from theopen top of the funnel 233.

When the valve means 241 are moved to the position shown by the dottedlines, thus closing the lower air intake orifices 215, the ducts 238communicate with the stacks 236. Operation of the fans 242 thereforeserves to draw the intake air through the upper air intake orifices 213,conveying it to the plenum 240 from whence it passes upwardly throughthe heat exchanger 211.

As was the case in the embodiment of FIG. 3, the stacks 236 arepositioned a sufficient distance from the discharged air so as to avoidinteraction therewith. The use of two or more stacks insures that atleast one of the stacks will be positioned upwind from the hot exhaustair. Suitable temperature sensors, motor controls and motor drivecircuits for the fans and the valve means may be provided, but are notillustrated for simplicity.

In FIG. 5, a cooling tower constructed in accordance with the inventionis shown in which the flow of air is reversed for day and nightoperations. Parts in the embodiment of FIG. 5 having a configuration andfunction similar to those of the embodiment of FIG. 2 have been givenidentical reference numbers preceded by a 3. In the embodiment of FIG.5, the duct means 312 consist of the funnel 333 and a horizontal conduit338. The conduit 338 terminates in an annulus 342 which surrounds thespace between the ground 314 and the lower edge of the funnel 333. Thetop of the annulus 342 is closed and a fan is provided in the duct orconduit 338. Alternatively, the fan could be placed in the funnel 333itself. The fan is a reversible fan and is suitably controlled by amotor, motor control circuit, and temperature sensors, not illustrated.The terminus of the conduit 338 furthest from the heat exchanger 311forms the lower air intake orifice 315. The upper air intake orifice 313is defined by the open top of the funnel 333.

Assuming the temperature sensors, not shown, indicate that cooler air isat ground level, the fans 344 rotate in a direction to force air asindicated by the solid arrows. Thus, air is drawn in through the lowerair intake orifice 315 and passes upwardly through the funnel 333 to bedischarged at the open top end thereof. In this case, the upper airintake orifice serves as a discharge orifice.

When the temperature sensors indicate that the temperature of the air asubstantial distance above ground level is cooler than the air at groundlevel, the direction of rotation of the fan 344 is reversed. This drawsair through the upper air intake orifice 313 as indicated by the dottedarrows. This air passes downwardly over the heat exchanger 311 andthrough the conduit 338 to be discharged therefrom through what wasformerly the lower intake orifice 315. Suitable baffles or other ductingconfigurations may be employed to prevent hot exhaust air from mixingback into the inlet. As an alternative to reversing the fan, thedirection of air flow could be reversed by suitable ducting and valvesat the fan.

The distance above the ground at which the upper air intake orifice isplaced in all cases is determined by accumulating specific data on thelapse rate effect with respect to the particular temperature-heightprofile of the cooling tower and its specific physical geographicallocation. Such data is dependent upon site location and time of day andyear and may be affected by the heat exchanger's total load. It isconceivable that the air flow provided in the cooling tower is of such amagnitude that the adiabatic lapse rate temperature profile may bealtered by the cooling tower itself. That is, hot ground air may beswept away so fast that cooler air from above the ground becomesavailable at ground level. If such is the case, the level of the upperair intake orifice may be closer to the ground than otherwise. Tofurther minimize the daytime effect of the super-adiabatic lapse rate,the ground surface surrounding the cooling tower may be covered withvegetation or a reflective material such as white crushed rock. Thiswill reduce heat absorption by the ground and subsequent heating of thecooling tower intake air.

It may be seen, therefore, that the invention provides an improvedperformance cooling tower capable of utilizing the effect of variationsin the adiabatic lapse rate adjacent the ground. More particularly, thecooling tower of the invention avoids the intake of hot air adjacent theground surface usually present at mid-day, while at the same time iscapable of utilizing the relatively cooler air present at ground levelduring the night-time. Thus, greater cooling efficiency may be achievedon a 24-hour basis.

Various modifications of the invention in addition to those shown anddescribed herein will become apparent to those skilled in the art fromthe foregoing description and accompanying drawings. Such modificationsare inteded to fall within the scope of the appended claims.

What is claimed is:
 1. A cooling tower comprising, a heat exchanger,duct means defining a passage for directing air over said heat exchangerfor cooling same, said duct means having an upper air intake orificepositioned a substantial distance above ground level and having a lowerair intake orifice positioned substantially at ground level so that saidupper and lower air intake orifices are vertically positioned apartsufficient to make air available adjacent the upper and lower air intakeorifices, and means for selectively drawing air into said duct meansthrough either one of said upper air intake orifice or said lower airintake orifice.
 2. A cooling tower according to claim 1 wherein saiddrawing means comprise movable valve means capable of opening one of theupper and lower air intake orifices to the duct means and effectivelyclosing the other of the orifices from the duct means.
 3. A coolingtower according to claim 1 wherein said drawing means comprise fanmeans.
 4. A cooling tower according to claim 1 including temperaturesensing means for sensing the air temperature at the level of each ofsaid upper and lower air intake orifices, and means responsive to saidtemperature sensing means for operating said drawing means such that airwill be drawn through the one of said air intake orifices at which thetemperature is the lower.
 5. A cooling tower according to claim 1wherein said duct means include an open top funnel having an annularintake region at ground level, and ancillary duct means communicatingtherewith, said ancillary duct means comprising a sleeve surrounding atleast a portion of said funnel coaxially thereof.
 6. A cooling toweraccording to claim 1 wherein said duct means include an open top funnelhaving an annular intake region at ground level, and ancillary ductmeans communicating therewith, said ancillary duct means comprising atleast one stack displaced from said funnel, the upper end of which formssaid upper intake orifice.
 7. A cooling tower according to claim 1wherein said duct means include an open top funnel having an annularintake region at ground level, and ancillary duct means communicatingtherewith, said drawing means comprising reversible fan means positionedin said ancillary duct means for directing the flow of air through saidduct means in either direction.